1. Field of the Invention
The present invention relates to a medical image display apparatus and medical image display system which execute noise addition simulation used before X-ray computed tomography.
2. Description of the Related Art
As is well known, an X-ray computed tomography apparatus is designed to obtain an image (tomogram) by calculating (reconstructing) the X-ray absorptance of a tissue such as an organ on the basis of the amount of X-rays absorbed in a subject to be examined as an index called a CT value with reference to the X-ray absorptance of water.
A reconstructed image inevitably contains image noise. Image noise is typically defined with reference to a variation in the CT value of a homogeneous phantom image as a standard deviation, which is generally called an image SD. In order to make diagnosis by observing a reconstructed image, e.g., to discriminate a shadow on the image as noise or a tumor, the image SD unique to the image must be considered.
In performing this X-ray computed tomography, a simulation image is sometimes generated by, for example, adding noise to an image obtained by past imaging operation to support decision of scan conditions under which a smaller dose of X-rays is allowed. An apparatus which realizes such support is called a scan plan simulator, with which a simulation image can be generated before CT scanning by inputting a region to be scanned, a body thickness, and scan conditions.
Note that a scan condition indicates at least one of the following: “scan mode”, “ON/OFF of an exposure reducing function”, “imaging slice thickness”, “image slice thickness”, “FOV”, “helical pitch”, “reconstruction function”, “tube voltage”, “tube current”, and “scan speed”.
The conventional scan plan simulator, however, has the following problems.
When simulation images are to be generated on a CT image basis, noise due to image reconstruction cannot be added. In addition, when simulation images are to be generated on a CT image basis, for example, artifacts originating from bones cannot be precisely reproduced theoretically. Therefore, for example, an unnecessarily good image SD (i.e., an unnecessarily high X-ray intensity) of an image obtained by actual imaging is obtained for an obtained simulation image. In contrast, a desired image SD cannot be obtained, and re-scanning is required. Either may lead to excessive X-ray exposure.